The present invention relates to novel urease and a process for the preparation thereof. Urease is used for the quantitative determination of urea and in artificial kidneys. The present invention is intended to prepare urease having suitable properties for the above purposes using thermophilic microorganisms.
Urease (EC 3.5.1.5) is an enzyme catalyzing decomposition of urea which results in the formation of ammonia and carbon dioxide and can be widely detected in plants, animals, microorganisms and so forth.
Urease derived from a jack bean and urease derived from microorganisms (see Japanese Patent Kokai Koho Nos. 86081/1983 and 17987/1984) have already been prepared on commercial scale and utilized in a clinical test reagent, an artifical kidney apparatus and so forth.
These known ureases, however, have a disadvantage of being ultimately unstable. In order to overcome this disadvantage of unstability, various methods have already been proposed.
Japanese Patent Kokai Koho No. 117488/1977, for example, discloses a method in which glutathione, ethylenediaminetetraacetic acid (EDTA) and citric acid salts are used in combination with urease. Japanese Patent Kokai Koho No. 138389/1972 discloses a method in which a thiol compound, a chelate reagent and an organic dibasic acid or its salt are used in combination with urease; Japanese Patent Kokai Koho No. 28498/1984, a method in which polyvinyl alcohol, N-acetylcystene and EDTA are used in combination with urease; and Japanese Patent Kokai Koho No. 82318/1984, a method in which in addition to the above substances, disaccharide is further used in combination. These methods, however, fail to sufficiently improve the stability of urease.
Enzymes derived from thermophilic microorganisms are generally considered to have advantages in that the stability is satisfactorily high and the cultivation period for the enzyme production is rather short. It has not yet been reported that urease can be successfully prepared using thermophilic microorganisms.